1. Field of the Invention
The present invention relates to direct injection diesel engines which inject fuel from a fuel injection nozzle provided on a cylinder head toward a combustion chamber provided on a piston top face section.
2. Description of Related Art
Various propositions have been made from the view points of, for instance, reduction of NOx, reduction of smoke, and reduction of fuel consumption rate in relation to the shape of a combustion chamber provided on a piston top face section of a direct injection diesel engine as well as to the type of fuel injection (Refer to, for instance, Japanese Utility Model Laid-Open Publication No. SHO 58-183933).
According to the utility model described in the aforesaid document, the combustion chamber comprises a troidal in a lower section of the combustion chamber and an open chamber section in an upper section of the combustion chamber, and by vertical movement of the piston in association with rotation of an engine, after a half of fuel is injected and led into the troidal in the lower section thereof, the remaining half is continuously led into the open chamber in the upper section thereof, and the fuels are separately and homogeneously distributed in the combustion chamber for the purpose of reducing both NOx and smoke simultaneously, as well as reducing the fuel consumption rate.
However, the fuel injection amount (namely the fuel injection period) should generally be changed according to the engine speed or the load of engine, and, consequently, the fuel injection timing (namely timing for start of injection) also should be changed.
With the disclosure in the document above, however, the fuel injection period is kept constant, and the ratio of fuel injection period is controlled only by incorporating a edge radius of a border section between a troidal and an open chamber each constituting a combustion chamber to a prespecified value. Therefore, in the document above, when a fuel injection period is largely changed, it is impossible to accurately distribute a half of the fuel to the troidal and a remaining half of the fuel to the open chamber, so that the effect in emission control and the effect in reduction of fuel consumption rate can hardly be expected.
Especially, in a case of an engine used for construction machines, a engine speed and the engine load are often largely changed, so that the capability of accurate fuel injection control in the situation as described above is desired.